The correct option is A Protista
Monera :
Sole members of kingdom monera are bacteria which are prokaryotes.
Protista :
All the unicellular or single celled eukaryotes are members of kingdom protista.
Fungi :
Members of kingdom fungi are eukaryotic multicellular organisms (except yeast).
Bacteria :
All types of bacteria are classified under kingdom Monera.
Conclusion :
All eukaryotic unicellular organisms are members of protista.
Final answer :
b. Protista